不均質層を有する金属材料の曲げ疲労寿命推定法に関する研究 層状不均質性と残留応力の効果に注目して

Abstract

It has often been reported that the hardening and compressive residual stress at surface were important factors for increasing fatigue strength of surface hardened materials. However, the effects of these two factors on fatigue lives were not always separated in previous experiments. Also it should be emphasized that no thorough investigation for these factors has been undertaken from a mechanical viewpoint.In the present study, the effects of laminated inhomogeneity and residual stress on bending fatigue lives were examined on the clad plates composed of low and medium carbon steels. On the basis of these experimental results, a method to estimate bending fatigue lives of the laminated inhomogenous metals was discussed. The main results obtained are as follows;(1) Cyclic bending stress-strain relation of the laminated inhomogeneous plates could be calculated approximately by applying the cyclic stress-strain relation of push-pull fatigue tests to the static bending deformation analysis.(2) Bending fatigue lives of the laminated inhomogeneous metals without residual stress could be estimated fairly well from S-N curves of the base metals by choosing the plastic strain amplitude (or strain amplitude) as an equivalent factor controlling the fatigue life. In the case with residual stress, the fatigue lives could be understood by adding an effect of residual stress on fatigue crack propagation lives after the microcrack initiation of fatigue to the estimation method mentioned above.